Blower door test reveals extent of building air leakage.

With today’s concerns for energy conservation and carbon footprint reduction, determining the energy efficiency of a building has become an essential cost-containing tool for the building owner. Properly installed insulation is one major contributing component to a building’s performance. Air leakage problems, however, are often overlooked. In many buildings, excessive air leakage is the biggest factor reducing energy-efficient performance.

Wasted energy and high heating and cooling costs are not the only problems caused by air leakage through the building envelope. According to a recent study of US commerical buildings: “...envelope leakage has several potentially negative consequences. These include uncontrolled and unconditioned outdoor air intake, thermal comfort problems, material degradation and moisture problems that can lead to microbial growth and serious indoor air quality problems.”(1)

		More About Air Leakage
		As the difference between indoor and outdoor air pressure in a building grows, air will leak out. The top areas and lowest floors of a building are areas with the biggest air pressure differences. Because warm and cold air rise and fall in a building, leaks in these areas are typically greater than elsewhere. The warm inside air will rise and leak out any unsealed areas near the top of the building. Cold outside air will seep in through breaches near the bottom of the building. If properly ventilated, relatively airtight buildings are more cost-efficient and provide better occupant comfort. Occupants experience fewer drafts, and it costs far less to maintain comfortable air temperatures and healthy air circulation. Proper airflow also helps preserve the quality of the building’s materials. As moist, heated air leaks into cooler insulated walls, ceilings and roofs, the warm vapor condenses on the cool surfaces creating an ideal environment for the growth of mold, mildew, and other unhealthy condensation conditions. These conditions can have an adverse effect on anyone with allergies and can be a contributor to “Sick Building Syndrome.”

By placing the building under a known pressure, a Blower Door test allows the technician to measure how much building airflow is required to maintain a certain pressure differential between indoors and outdoors. The number of air changes per hour (the complete replacement of the indoor air volume of the building in one hour) at a standard pressure differential (interior pressure compared to exterior pressure, measured in Pascals) reveals the building envelope's air leakage profile.

Blower Door measurements can also be used to estimate the natural infiltration rate of buildings. While the Blower Door doesn't measure infiltration rates directly, test results can be used along with mathematical models to estimate annual average and design infiltration rates for the purposes of estimating the efficiency of the building envelope, evaluating indoor air quality, estimate the need for mechanical ventilation, and to help with proper sizing of heating and cooling equipment.

A Blower Door consists of powerful variable-speed fan units mounted in an adjustable panel that temporarily fits in a doorway. Pressure gauges connected to the fan measure the rate of airflow required to maintain the building at a certain pressure. This controlled airflow enables the technician to both find and measure air leakage in the building envelope.

A basic Blower Door system includes three components: calibrated fan units, a door-panel system, and a device to measure fan flow and building pressure. The Blower Door fan is temporarily sealed into an exterior doorway using the door-panel system. The fan is used to blow air into or out of the building, which creates a small pressure differential between inside and outside. This pressure imbalance forces air through all holes and penetrations in the building enclosure. By measuring the airflow through the fan and its effect on the air pressure in the building, the Blower Door test measures the air tightness of the entire building envelope.

Scientific studies and practical experience tell us that commercial and institutional buildings often have significant air leakage problems, regardless of their age, size or construction. Blower Door testing, which was originally developed as a research tool for scientists, is now a standardized method for assessing the integrity of the building envelope. It is widely recognized as an efficient and cost-effective tool in the quest to to improve building energy efficiency, reduce carbon emissions, and enhance indoor air quality.

1. Airtightness of Commercial Buildings in the U.S., Emmerich and Persily, National Institute of Standards and Technology, Gaithersburg, MD